Generally in the die-casting art, it is essential to accurately control the feeding amount of the molten metal in order to improve a quality of castings and an efficiency of operation.
The fluctuation of the feeding amount of the molten metal depends on that of a suction head of an electromagnetic feed pump for pressurizing the molten metal out, so that it is required to control the capacity of the pump relatively to the fluctuation of the suction head or to maintain the suction head at constant in disregard of the feeding process.
Hithertobefore, the capacity of the pump has been usually controlled by changing the electromagntic voltage or the actuating period of the pump, while in order to maintain the suction head at constant, a complete-closed type furnace has been employed to pressure the whole furnace as predetermined or a half-closed type furnace wherein the feeding chamber and/or the discharge chamber are open has been employed to pressure the whole furnace as predetermined so as to keep the molten metal in the feeding chamber or the discharge chamber at a fixed level.
Each conventional method as above-mentioned, however, had the following disadvantages.
The method for controlling the capacity of the pump is required to operate or compute the electromagnetic voltage or the actuating period of the pump by stages relatively to the fluctuation of the suction head, resulting in a complicated structure. Furthermore, especially when the actuating period is changed, the actuating cycle of the casting process is also changed, thereby lowering the operation efficiency and the quality of castings.
With regard to the method for maintaining the suction head at constant, on the other hand, the complete-closed type furnace has a complicated structure with an inferior maintenance, while the half-closed type furnace has a simpler structure with a comparatively convenient maintenance than the complete-closed type. The half-closed type furnace, however, has a dangerous disadvantage such that the molten metal may overflow from the feeding chamber or the discharge chamber owing to a mis-operation of the apparatus and further it is difficult to accurately keep a level of the molten metal at constant when one shot of the feeding amount is smaller as die-cast machines.
Accordingly, an object of the invention is to solve the above problems and to provide a holding furnace of constant molten metal level capable of precisely and firmly keeping a level of the molten metal without overflow thereof in a half-closed type furnace with a simple structure with a convenient maintenance.